The present invention relates to an automatic transmission to be mounted on a vehicle.
Generally, automatic transmissions mounted on vehicles include a transmission mechanism having a plurality of planetary gear sets (planetary gear mechanisms) and a plurality of friction fastening elements, such as clutches and brakes. Such an automatic transmission selectively fastens one or more of the friction fastening elements to switch a power transmission path among a plurality of paths which pass through the planetary gear sets, respectively, so as to achieve a predetermined gear position corresponding to an operating state of the vehicle.
For example, JP2004-183705A discloses an automatic transmission including three single-pinion-type planetary gear sets and five friction fastening elements, for achieving six forward gear positions and one reverse gear position by fastening two of the friction fastening elements.
Further, in terms of a configuration of the power transmission path, an automatic transmission is known, which includes a double-sun-gear-type planetary gear set in which a sun gear is divided, in axial directions thereof, into first and second sun gears, and a carrier body supporting a pinion shaft of a carrier is coupled, by passing between the first and second sun gears, to a rotational member disposed on an inner circumferential side of the first and second sun gears.
As illustrated in FIG. 7, with the automatic transmission 110 disclosed in JP2004-183705A, a double-sun-gear-type planetary gear set 120 is disposed on a counter-drive-source side inside a transmission case 111, and the planetary gear set 120 has coaxial first and second sun gears 121 and 122, a ring gear 123, a pinion 124 meshed with the first and second sun gears 121 and 122 and the ring gear 123, and a carrier 125 supporting the pinion 124.
The carrier 125 has a pinion shaft 126 rotatably supporting the pinion 124, and a carrier body 127 supporting both end parts of the pinion shaft 126. The carrier body 127 is provided with a power transmitting part 127a extending inward in radial directions of the planetary gear set 120 by passing between the first and second sun gears 121 and 122.
With the planetary gear set 120, the first sun gear 121 is coupled, via a power transmitting member 132, to a brake hub 131 of a brake 130 disposed on an outer circumferential side of the planetary gear set 120, the second sun gear 122 is coupled to a sun gear 141 of a planetary gear set 140 disposed on a drive source side of the planetary gear set 120, the carrier 125 is coupled, via the power transmitting part 127a, to a center shaft 142 disposed on an inner circumferential side of the first and second sun gears 121 and 122, and the center shaft 142 is coupled to a clutch disposed on the drive source side of the planetary gear set 140. Note that the reference numerals used here to describe the automatic transmission disclosed in JP2004-183705A are not in correspondence with those in JP2004-183705A.
Meanwhile, in such an automatic transmission including a double-sun-gear-type planetary gear set, a pinion constituting the double-sun-gear-type planetary gear set has a smaller diameter than a sun gear and a ring gear and rotates at high speed, and therefore, a sufficient amount of lubricant oil needs to be supplied to bearings, such as needle bearings, provided between the pinion and the pinion shaft, in order to secure high performance, durability, etc.
When supplying the lubricant oil to the bearings provided between the pinion and the pinion shaft, generally, the lubricant oil is supplied from an oil supply hole formed on a side of a central axis of the transmission mechanism, to spread to a space therearound by a centrifugal force, then is captured on an outer circumferential side of the space to be introduced into an oil path inside the pinion shaft, and guided, from the oil path, to the bearings which are on an outer circumferential side of the pinion shaft.
Also in the planetary gear set 120 in FIG. 7, an oil supply hole 121a is formed in a part of the first sun gear 121 on the counter-drive-source side. As indicated by a lubricant oil supply path L11, lubricant oil is spread from the oil supply hole 121a to a space 128 formed therearound, is captured on an outer circumferential side of the space 128 to be introduced into a carrier body oil path 127b, and is supplied, through a pinion shaft oil path 126a, to bearings 129 provided between the pinion 124 and the pinion shaft 126.
However, after the lubricant oil from the oil supply hole 121a is supplied to the space 128 inside the transmission case 111, only a portion of the lubricant oil is introduced into the carrier body oil path 127b to be supplied to the bearings 129, which lowers lubricant oil supply efficiency. Therefore, to supply a predetermined amount of lubricant oil to the bearings 129, a supply amount of the lubricant oil needs to be increased, which may cause a size increase of an oil pump, an increase of driving loss, etc.